1. Field of the Invention
The present invention relates to a CATV conditional access system in which digital programs are provided in a batch mode from a single digital head end to a plurality of areas.
2. Description of the Related Art
Very recently, community antenna television sysetms (CATVs) are popularized while multi-media have been developed.
As indicated in FIG. 8, this conventional CATV system is arranged as follows. That is, an analog head end (control center) 1 is installed in each of areas, terminals 2 set into homes of subscribers are connected via cables 3 to this analog head end 1, and then an analog picture signal (video/audio signal) is distributed from this analog head end 1 to the respective terminals 2 via a predetermined picture frequency channel.
Contrary to such an analog CATV system, a digital CATV system will be popularized, because of various needs, for instance, multi-channel broadcasting system, video-on-demand (VOD), and bidirectional communications.
While such an analog CATV system is transferred to a digital CATV system, in the case that an operation station of an existing analog CATV system starts a digital CATV broadcasting service, this operation station is required to commence distributions of digital picture signals without interrupting the distribution services to the subscribers which presently receive the existing analog broadcasting programs.
To meet such a need, the applicant of the present application has proposed such a novel digital integration type CATV system as shown in FIG. 6, since the investiment amount required in such a case that the operation station of the existing analog CATV system is transferred from the analog CATV system to the digital CATV system is reduced, and further, the problem such as the installing space occurred when the digital CATV system is newly installed is solved. Accordingly, the present analog CATV system can be smoothly transferred to the digital CATV system.
In this digital integration type CATV system, one digital head end 10 is installed with respect to a plurality of analog head ends 1A, 1B and 1C, and then this digital head end 10 will supply digital programs in a batch mode to the respective analog head ends 1A, 1B and 1C. The plural analog head ends 1A, 1B and 1C are installed in the respective areas A, B and C where the existing analog CATV system has been constructed.
Then, picture signals of digital programs transmitted from this digital head end 10 are distributed by the respective analog head ends 1A, 1B and 1C via the cables 3 to the respective terminals 2 provided in the areas, in combination with the analog programs distributed from these analog head ends 1A, 1B and 1C, while using an empty channel thereof.
In this case, as to an MPEG TS (Transport Stream) used to transmit a picture signal of a digital program, picture signals of plural channels are usually multiplexed on a single stream.
As a result, in the above-explained so-called “digital integration type CATV system”, when the digital head end 10 provides the digital programs in a-batch mode, even if the structures of the digital programs are different from each other in the respective areas, then the same digital programs having the different program structures would be distributed to all of these areas A, B and C, as illustrated in FIG. 7.
As a consequence, when a digital integration type CATV system is accomplished, structures of digital programs should be unified in each area. Also, even when the structures of the digital programs are not unified, since such a digital program which is not provided in each of the areas is distributed from each of the analog head ends to terminals, the following problem necessarily occurs. That is, only uniform services of the digital programs can be allowed to be provided in the respective areas.